Anode for sputter coating

ABSTRACT

A sputtering anode is disclosed wherein the anode is in the form of a container or vessel; and, wherein the conducting surface communicating with a cathode is the inside surface of the container or vessel. The anode can be mounted outside of a coating chamber having its opening communicating with the chamber or alternatively may be mounted within the chamber. The anode may be an inlet port for receiving inert gas for use in forming the plasma and for pressurizing the anode.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 11/074,249 filed Mar. 7, 2005, which claimspriority from U.S. patent application No. 60/603,211 filed Aug. 20,2004, both of which are incorporated herein by reference for allpurposes.

FIELD OF THE INVENTION

This invention relates generally to an apparatus and method fordepositing films on a substrate, and more particularly to a reactivemagnetron sputtering device and technique for depositing materials ontosubstrates in which the deposited films have predictive thicknessdistribution and in which the apparatus can operate continuously andrepeatedly for very long periods.

BACKGROUND OF THE INVENTION

In a sputtering deposition process ions are usually created bycollisions between gas atoms and electrons in a glow discharge. The ionsare accelerated into the target cathode by an electric field causingatoms of the target material to be ejected from the cathode surface. Asubstrate is placed in a suitable location so that it intercepts aportion of the ejected atoms. Thus, a coating of target material isdeposited on the surface of the substrate.

Sputter coating is a widely used technique for depositing a thin film ofmaterial on a substrate. Sputtering is the physical ejection of materialfrom a target as a result of gas ion bombardment of the target. In oneform of this technique, known as DC sputtering, positive ions from aplasma discharge formed between an anode and a target cathode areattracted to and strike the target cathode, dislodging atoms from thetarget surface of the cathode thereby providing sputtering atoms. Someof the dislodged atoms impinge on the surface of the substrate and forma coating. In reactive sputtering a gaseous species is also present atthe substrate surface and reacts with, and in some embodiments combineswith, the atoms from the target surface to form the desired coatingmaterial.

The sputtered material is also deposited on any other surface exposed tothe sputtered atoms. It is recognized in the prior art that if thecoating is an electrically insulating material, such as a metal oxide,the build up of the material on other parts of the sputtering apparatuscan cause problems. In particular, the build up of an insulating coatingon the anode interferes with the ability of the anode to removeelectrons from the plasma, as required to maintain the plasma's chargebalance. This destabilizes the plasma and interferes with depositioncontrol. As a result, it is common to use a different sputteringtechnique, for example RF sputtering, to deposit layers of insulatingmaterials. However, RF sputtering is a less efficient, lesscontrollable, slower and more expensive process than DC sputtering.

In operation, when the argon is admitted into a coating chamber, the DCvoltage applied between the target cathode and the anode ignites theargon into a plasma, and the positively charged argon ions are attractedto the negatively charged target. The ions strike the target with asubstantial energy and cause target atoms or atomic clusters to besputtered from the target. Some of the target particles strike anddeposit on the wafer or substrate material to be coated, thereby forminga film.

In an endeavor to attain increased deposition rates and lower operatingpressures, magnetically enhanced targets have been used. In a planarmagnetron, the cathode includes an array of permanent magnets arrangedin a closed loop and mounted in a fixed position in relation to the flattarget plate. Thus, the magnetic field causes the electrons to travel ina closed loop, commonly referred to as a “race track”, which establishesthe path or region along which sputtering or erosion of the targetmaterial takes place. In a magnetron cathode, a magnetic field confinesthe glow discharge plasma and increases the path length of the electronsmoving under the influence of the electric field. This results in anincrease in the gas atom-electron collision probability thereby leadingto a much higher sputtering rate than that obtained without the use ofmagnetic confinement. Furthermore, the sputtering process can beaccomplished at a much lower gas pressure.

As mentioned heretofore, in DC reactive sputtering, a reactant gas formsa compound with the material which is sputtered from the target plate.When the target plate is silicon, and the reactive gas is oxygen,silicon dioxide is formed on the surface of the substrate. However,because silicon dioxide is a good insulator, a film thick enough tocause arcing is rapidly formed in areas outside of the race track, e.g.on electrically grounded dark space shields. Silicon dioxide is known tobe one of the most difficult dielectric films to deposit by magnetronreactive sputtering because of this characteristic. The arcingassociated with silicon dioxide has prevented planar magnetron reactivesputtering from being efficiently utilized to deposit high qualitysilicon dioxide films. One aspect of this invention provides a coatedcathode having its sides and bottom surface coated with a dielectric tolessen or obviate arcing.

In operation, due to the accumulation of dielectric material in variousparts of the coating chamber, it has been necessary to clean the systemon a regular basis. Indeed, when coating silicon dioxide or siliconnitride by reactive sputtering, typical systems can only operatecontinuously for relatively short periods of time.

Finally, another limitation to the utility of planar and cylindricalmagnetrons in either reactive or non-reactive sputtering is that filmsdeposited by sputtering have not achieved the degree of uniformity orrepeatability required for many high precision applications.

There have been many attempts to ameliorate these unwanted effects ofmagnetron sputtering. For example “bottle-brush” anodes have beenproposed and are described in U.S. Pat. No. 5,683,558 in the name ofSieck et al, issued Nov. 4, 1997. This kind of anode advantageouslyprovides a large surface but, depending on its position relative to thetarget, it becomes non-uniformly coated over time and causes the anodeto move to other surfaces in the deposition system. Additionally, thedistance between the brush needles is very close and often leads to anincreased anode voltage, especially at low pressure.

Anode plates and ring designs have been described by F. Howard Gilleryet al., PPG Industries Inc., in U.S. Pat. No. 4,478,702, entitled “Anodefor magnetic sputtering apparatus”, and in U.S. Pat. No. 4,744,880,entitled “Anode for magnetic Sputtering of gradient films”, and by P.Sieck in “Effect of Anode Location on Deposition Profiles for LongRotatable Magnetrons”, SVC, 37th Annual Technical Conf. Proceed., 233,(1994).

Anode plates and ring designs described by J. R. Doyle, et al., inJ.Vac. Sci. Technol. A12, 886 (1994) are the most widely used design foranodes. Typically the anode is in close proximity to the cathode toenable a sufficient coupling of the anode-to-cathode plasma. Most oftenthe gas inlet is close to the target surface to increase the targetpressure locally. Most of the time the anode surface is also close tothat location which increases the plasma coupling and reduces the anodevoltage. Unfortunately these types of anodes can't be positioned too farbehind the cathode, because the electrons have to cross magnetic fieldlines on route to the anode which adds a high resistance and increasesthe anode voltage. On the other hand, having the anode close to thecathode surface increases the anode's susceptibility to being coatedwith sputtered material thereby making the anode unstable.

It is known to position dispose the anode in close proximity to otherplasma sources out of the direct line of sight of the cathode. Thisapproach works for relatively thin coatings, for example coatings ofless than 5 μm, but for thicker films the anode becomes coated as welldue to gas scattering. This makes it necessary to routinely exchange theanodes, which increases the cycle time and adds to the cost.

One disadvantage to the aforementioned approaches is that the size ofthe anodes has to be relatively large to work at a reasonably lowvoltage. The large size leads to an uneven contamination of the anodesurface and to a change in sputter distribution. Furthermore, a largeanode has to be accommodated within the coating chamber where space istypically lacking.

A small filament-like anode is another form of prior art anode. Thisanode requires relatively high voltages for example, greater than 70 V,which typically leads to undesirable sputtering of surfaces at or nearthe anode. The anode has to be positioned very close to the cathode forsufficient coupling. Additionally, major changes to the magnetrongenerally have to be made by way of shunting the magnetic fields closeto the anode.

Dual magnetron AC sputtering has been proposed by S. Schiller, K.Goedicke, V. Kirchhoff, T. Kopte in “Pulsed Technology—a new era ofmagnetron sputtering”, 38th Annual Technical Conference of SVC, (1995).

This approach inherently solves the moving anode and disappearing anodeproblems of some of the aforementioned prior art anodes, but thesputtering rates are usually lower and AC sputtering needs a higherpressure to run at decent cathode voltages <900 V. This increases thegas scatter and thus the defect growth. But even at ‘low’ averagevoltage the peak voltage in this setup is very high and often greaterthan 1000 V and leads to an increased compressive stress in the coating.The high voltage is caused by igniting the plasma every half-cycle ateach cathode.

The very recent approach of Dual anode magnetron sputtering to solve theanode problem uses a dual anode AC configuration. Preliminary testsshowed that the anodes have to be highly coupled into the cathodeplasma. Thus, they have had to be positioned very close to the cathode.Because the anode reaches very high negative voltages, this causessputtering from the anode during the cleaning cycle. In a paper entitled“Redundant Anode Sputtering: A Novel Approach to the Disappearing AnodeProblem”, published on the internet at the following website: http://wwwadvanced-energy.com/upload/white2.pdf, several disadvantages of Dualcathode AC sputtering are mentioned.

Since the anode is generally close to the target, it is exposed tocoating material. In practice, in many prior art systems, anodes have tobe exchanged or cleaned at frequent, regular intervals. Even when theanode is out of a direct line of sight of the direct material flux, theanode becomes coated due to gas scattering of coating material.

It is an object of this invention to provide an anode that is extremelywell shielded from coating material. The provision of such an anodeleads to a more stable sputtering process, especially for very thickcoatings, and reduces or eliminates the maintenance of the anode. Thisreduces the cycle time and labor costs in coating substrates.

It is a further object of this invention to provide an anode which canbe pressurized and which requires a lower voltage than many prior artanodes. Although the anode can be pressurized, it operates within orcommunicates with a chamber under vacuum.

It is a further object of this invention to provide an anode whereinlittle or no arcing at or near the anode occurs.

It is yet a further object of this invention to provide a preferredcathode for use with the anode of this invention.

SUMMARY OF THE INVENTION

In accordance with the invention, there is provided an apparatus anodefor use in the sputtering of a material, comprising at least one anodedefining a vessel having an opening to an electrically conductive innerbody and having an outer body, the electrically conductive inner bodybeing coupled to a voltage source to provide a voltage differencebetween the sputtering material and the conductive inner body.

In accordance with an aspect of the invention there is provided asputtering apparatus anode for use in the sputtering of a material,comprising:

at least one anode defining a substantially closed vessel comprising oneor more sidewalls and a bottom wall, said vessel having an opening to anelectrically conductive inner body and having an outer body, wherein theinner and outer body are at a same electrical potential and are formedof the one or more sidewalls and bottom wall, such that the inner bodyis the inside one or more sidewalls and bottom wall of the vessel and anoutside one or more sidewall forms the outer one or more sidewalls andouter bottom wall of the vessel, the electrically conductive inner bodybeing coupled to a voltage source for providing a voltage differencebetween the sputtering material and the conductive inner body, whereinthe inner body of the vessel is for receiving and collecting electronsor negatively charged particles passing through the opening, wherein theopening to the electrically conducting inner body is so located forcommunicating with a coating chamber and wherein the anode iselectrically isolated from the coating chamber and electricallyconnected to a positive potential, wherein the opening of the vessel ispolygonal shaped.

In accordance with an aspect of the invention, there is provided, asputtering apparatus anode for use in the sputtering of a material,comprising at least one anode defining a vessel having an electricallyconductive inner body and an outer body, the electrically conductiveinner body being coupled to a voltage source for providing a voltage tothe inner body.

In accordance with another aspect of the invention there is provided acoating chamber including a cathode, the chamber having in communicationtherewith, an opening of an end of an anode in the form of a vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will now be described inaccordance with the drawings, in which:

FIG. 1 a is a cross sectional view of a small portion of a coatingchamber in accordance with an embodiment of the invention including acylindrical hollow anode with a length h, diameter d and an orificeopening do at an end of the anode coupled to an opening in the coatingchamber;

FIG. 1 b is a cross sectional view of a coating chamber in accordancewith an embodiment of the invention including a cylindrical hollow anodewith a length h, diameter d and an orifice opening do at an end of theanode, wherein the anode is located shown within the coating chamber;

FIG. 1 c is an alternative embodiment of the anode wherein the openingof the anode is at a side thereof, or side end of the anode.

FIG. 1 d is an isometric view of an anode having a single opening at anupper end thereof.

FIG. 1 e is an isometric view of an anode having a single opening in aside thereof.

FIG. 1 f is an isometric view of an anode a cathode a distance d awayfrom the anode opening.

FIG. 2 is a graph illustrating the dependence of anode voltage on thesize of the anode;

FIG. 3 is a graph illustrating the effect of anode voltage versusdistance from a grounded surface close to the powered anode;

FIG. 4 is a graph illustrating pressure dependence of the anode voltagewherein the arrows indicate the pressure region in a typical sputteringprocess;

FIG. 5 is a graph illustrating anode voltage versus the area of theanode opening into the chamber for two different gas flows into theanode; and,

FIG. 6 is a graph comparing the anode voltage versus time for a copperanode and a stainless steel anode.

FIG. 7 is a cross sectional view of an anode in accordance with anembodiment of this invention wherein the anode is connected to a powersupply.

FIG. 8 is a diagram of a coating apparatus having two externally mountedanodes in accordance with an embodiment of this invention.

FIG. 9 is a graph depicting the standard deviation of the opticalthickness of SiO2 of five consecutive coating runs measured at differentvertical positions in a MetaMode® coating machine without an anodeillustrated by the black, solid graph and of five consecutive coatingruns with 2 powered anodes as shown in gray, open symbols.

FIG. 10 a is a plan view of a coating machine having multiple anodes andan elongated cathode in accordance with an embodiment of the invention.

FIG. 10 b is an end view of the coating machine shown in FIG. 10 awherein the elongated cathode is cylindrical

FIG. 10 c is an end view of the coating machine of FIG. 10 a wherein thecathode is a planar cathode.

FIG. 11 is a view of a preferred cathode having its sides except for thetarget side insulated with a dielectric insulator adjacent to an anodedisposed within a coating chamber in accordance with an embodiment ofthis invention.

DETAILED DESCRIPTION

Referring now to FIG. 1 a an anode 10 is shown in the form of acontainer or vessel having conductive walls of copper or stainless steel12 having an opening 14 at a first end for communicating with a vacuumchamber to which it is directly coupled. The copper or stainless steelwalls define the inside of the container vessel or inner body of thecontainer. The outside walls of the container are referred to hereafteras the outer body. The outer body may be coated with a suitable coatingso as to be electrically insulated. In the cross sectional view watercooling pipes 16 are shown substantially around the anode formaintaining the temperature of the anode in operation. A gas inlet port18 is shown for providing a conduit into which gas may enter the anodecavity to pressurize the anode. A ground cover 21 is placed around theanode and cooling pipes and is at ground potential. In operation theanode is pressurized with argon gas which promotes the formation ofplasma in the presence of a suitable ignition voltage and maintenancevoltage thereafter. The anode 10 is essentially a conducting container,which in a preferred embodiment is mounted onto the vacuum chamber;alternatively, it may reside within the vacuum chamber. The anode shownin FIG. 1 a was designed to function with a low anode voltage and littleor no arcing. It is preferred that the anode be at a voltage of 10 to 60volts above ground or above the cathode chamber voltage and morepreferably a low anode voltage of approximately 30 volts is preferred toreduce process variation.

Referring now to FIG. 1 b, an anode similar to the one shown in FIG. 1 ais shown, wherein the entire anode body 10 b, 21 b is shown disposedwithin a vacuum coating chamber and wherein the opening 14 b having adiameter d0 is for communicating with the target cathode sputteringmaterial within the vacuum chamber. Water cooling tubing 16 b is shownhaving inlet and outlet ports entering and exiting from outside thevacuum chamber. The Ar-gas port 18 b is shown to communicate with theanode and supply the anode with gas from outside the vacuum chamber.Notwithstanding the anode is considered to be a closed vessel with theexception of the opening 14 b for receiving electrons. An insulator 19 bensures the anode is electrically insulated from the chamber wall and apower supply is shown to provide a voltage difference between the anodeand cathode or cathode material within the chamber. The e anode is at ahigher potential than the chamber wall so that electrons will flow intothe anode opening rather than being attracted to the chamber walls.

FIG. 1 c shows an alternative embodiment wherein an anode having copperwalls 12 c have an opening 14 c at a different location which is at theside of the cylinder. In this embodiment the anode can be mounted withinor external to the vacuum chamber. Water cooling pipes 16 c, and Ar-gasport 18 c are provided.

Referring now to FIG. 1 d a cylindrical shaped vessel 142 forming ananode is shown having a single opening 144 at an end thereof wherein theopening 144 is circular in shape forming a polygon. Thus, when lookinginto the opening from outside of the vessel one can see an openinghaving a shape of a circle. For the purposes of this specification theterm polygon shall include all bounded n-sided shapes including shapeswherein n approaches or is ∞ such as circles and ellipses and otherclosed smooth shapes; thus the circular shaped opening of this inventionforms a polygon.

FIG. 1 e. Illustrates the relationship between the largest opening “a”or diameter of the vessel 142 and the angle α formed with respect to thedistance of the opening from a cathode 145. The angle α is 90 degrees orless and preferably 70 degrees and most preferably about 20 degrees.Although in many of the figures the opening is shown directly facing thecathode this is not a requirement.

In a preferred embodiment of the invention, the vessel forming theanode, for all intents and purposes forms a closed vessel having anopening at an end or side thereof for allowing electrons to passtherethrough. In some instances a supply line for providing a gas to theinside region of the anode is present, however the vessel is asubstantially closed vessel other than having an opening for allowingelectrons to pass therethrough. Structures such as channels or cylindersopen at opposite ends which are substantially open structures are notconsidered within this specification to be vessels. A vessel is astructure capable of holding a fluid albeit having an opening forallowing the fluid or as it be in the instant invention, allowingelectrons to flow thereinto from the cathode. In a preferred embodimentof this invention the vessel is preferably free of physical structureswithin it that would obstruct electrons from entering the vessel andreaching the inner sidewalls of the vessel; thus the vessel ispreferably a relatively smooth walled jug, jar, or box type vesselhaving no physical structures within and having a single opening forallowing electrons to pass thereinto. In most instances the singleopening has a polygonal shaped cross section. However the opening may beformed in a side wall of a cylindrical vessel which would have apolygonal shaped opening.

Referring to FIG. 7 circuitry is shown which allows three switchablemodes of electrical operation of the anode 70. The switch 72 allowsswitchable selection between ‘floating’, ‘grounded’, and ‘biased’operation.

In floating operation the potential of the anode relative to ground isself adjusting. In this instance the anode voltage depends upon theplasma impedance. For DC sputtering the typical anode voltage ismeasured to be between +20V and +55V, whereas the cathode voltage can beanywhere between −300V and −700V, depending upon which materials arecoated and which process parameters are used. Sometimes a resistor isprovided between the ground and the anode to protect the system in caseof a catastrophic breakdown.

In grounded operation mode the anode is connected to chamber ground. Tobe the preferred return path for the electrons, the anode needs to havesuperior conductivity over other grounded chamber components. Feedingprocess gas into the anode decreases the plasma impedance to the anode.

In biased operation the anode potential relative to ground is determinedby a power supply. A voltage range of +20 to +55V makes the anode thepreferred return path for electrons while maintaining a constant andrepeatable operation.

To minimize the anode voltage in the preferred floating mode, a minimumanode surface area as shown in FIG. 2 is required. Additionally,grounded surfaces have a major impact on the plasma impedance and thusthe anode voltage. The results of experiments illustrated in FIG. 3 showthat the closest grounded surface should be at least 25 mm away for thisspecific process parameter set.

The pressure dependence of the anode voltage is shown in FIG. 4. Thearrows indicate that the sputtering pressure does not always coincidewith the optimum pressure for the powered anode.

The optimum anode parameters, that is, area, anode ground distance, andpressure, led to the embodiment where the anode surface is the inside ofa container or vessel. In this preferred embodiment, the anode comprisesa tube with a diameter of at least d=10 cm and a length of at least h=20cm as shown in FIG. 1.

For low scattering processes the chamber pressure is below 2 mTorr. Ahigh pressure at the anode is achieved by reducing the orifice oropening 14 of the anode 10 and feeding the process gas into the anodevia the inlet port 18. Since small orifices constrict the plasma leadingto a reduction in electrical conductivity and thus to an increase of theanode voltage, it was discovered that an optimum opening has an area ofabout 20 cm2 and is preferably round. This relationship is depicted inFIG. 5.

The anode can be made of a plurality of conducting materials. The impactof the anode material on the anode voltage is illustrated in FIG. 6.This graph illustrates that copper results in a 2 V lower anode voltagethan stainless steel.

Since the anode can be mounted outside of the vacuum chamberadvantageously it does not use up any space within the vacuum chamberand needs fewer vacuum components. By way of example, standard anodesneed at least an additional electrical feed-through. The anode 10 shownin FIG. 1 is electrically insulated from the grounded chamber wall byway of an insulating material 19 shown. This is important since it ispreferred for the anode to be able to have a free floating voltage whichwill typically be greater than that of the grounded chamber wall.

Advantageously, electrical and water feed-through connections and gaslines 18 can be mounted from the outside.

When the container anode is used as an external anode, the thickness ofthe walls have to be sufficient to withstand the atmospheric pressure;in the instance when the anode serves as an internal anode the anode canbe quite thin as long as the anode does not become too highlyelectrically resistive.

In operation the anode can be pressurized to more than 3 mTorr. It isexpected that this anode 10 can run in nearly continuous operation forextended periods of time; experiments have been carried out running thisanode for more than 2000 hours continuously without having to take theanode 10 out of service to be cleaned or changed, and it is believedthat it is possible to operate the anode for more than 10000 hours ofcontinuous operation.

Although it is preferred to electrically insulate the outside of theanode container when part or the entire anode is within the coatingchamber, it is not absolutely essential. Without any insulator on theoutside of the anode, anode plasma in the orifice was observed and a lowanode voltage was measured. Since the outside of the anode may act as ananode, when it is un-insulated, it would likely become coated over time,thereby changing the location of the anode which will effect thedistribution and rate of sputtered particles at the cathode. Hence, itis preferable to electrically insulate the outside of the anode. Theinsulation of the outside can be a coating on the anode body, butalternatively can be an additional cover 21 b as shown in FIG. 1 b. Thecover 21 can be grounded or floating.

The novel anode in accordance with this invention has several advantagesover known anodes used in sputter coating:

a) In accordance with this invention, the active anode area or surfaceis on the inside of a container, which substantially protects the anodefrom sputtered material. This greatly contributes to process stability,because the properties of the anode surface and thus the plasma,location and conductivity do not change during a coating run, and arerelatively constant from coating run to coating run.

b) The small orifice or container opening further reduces the chances ofcoating material finding its way to the anode surface. It also definesthe location of the anode very well.

c) The small orifice or opening and gas inlet port locally increases thepressure inside the anode and thus reduces the anode voltage. Theprovision of Argon process gas into the anode increases the pressurelocally inside the anode and further decreases the anode voltage withoutsignificantly increasing the chamber pressure.

d) The large surface (>1800 cm2) of the anode further reduces the anodevoltage

e) The spherical or cylindrical shaped anode increases the volume of theanode and also the distance between anode surfaces and eliminatesgrounded surfaces close to the active anode surface.

f) Water-cooling further adds to the stability of the anode. It reducesthe change of the anode behavior due to an external temperature shift ordue to excessive heating of the anode by a large anode current.

g) The anode of this invention usually does not need a second plasma,except the one from the cathode, to work at low voltages.

It should be noted that numerous other embodiments may be envisagedwithout departing from the sprit and scope of the invention. For exampleFIG. 8 illustrates one of many possible anode configurations forelongated cathodes as used in a MetaMode® configuration. In thisembodiment two anodes 72 a, 72 b are positioned symmetrically at thesides of a long planar Si cathode 74. Using this configuration therun-to-run variation in place of previously used configurations can beimproved from a standard variation of 1.64% to 0.22%. This isillustrated in the graph shown in FIG. 9.

In a paper entitled “Active Control of Anode Current Distribution forD.C. Reactive Sputtering, of SiO2 and Si3N4” by P. Sieck published inSurface and Coatings Technology, 68/69, (1994) 794-798, incorporatedherein by reference, methods for controlling the current distributionare described with respect to in-line coating systems.

The instant invention is believed to be applicable to this and othersuch in-line coating systems; for example it is believed that the use ofmultiple nodes could be used in such in-line coating systems. By way ofexample, the hollow anode described heretofore in accordance with thisinvention, could increase the performance of the anode arrangementscheme described in this publication by Sieck; by using the anode ofthis invention:

-   1) the active anode surface is protected from coating material,-   2) anode locations are better defined,-   3) gas-inlets are well defined;

Depending on the length of the cathode and space available in themachine one could have several anodes along the cathode which either arecontrolled electrically or wherein the gas flow through the anode isadjusted through the anode cavity to control the sputter distributionalong the length of the cathode. Such adjustments could be done in-situduring a coating run, for example, with a feedback loop from in-situspectral measurements.

Referring now to FIG. 10 a a plan view is shown of a coating machinewith an elongated cathode 101 having anodes 102 through 107 disposedabout the anode. FIG. 10 b is an end view of FIG. 10 a wherein theelongated cathode 101 is a cylindrical cathode having independent gasinlets 120 a and 120 b. FIG. 10 c is an end view of FIG. 10 a whereinthe cathode is a planar cathode.

In addition to providing a novel and inventive anode, an ever-increasingdemand for low defect concentration in coated devices such as opticalfilters, mirrors, and semiconductor circuits requires a cathode thatwill have little or no arcing at the sputtering target. At presentcommercially available cathodes and also cathode designs described inprior art lack this important feature, especially when the depositionrate is being kept high.

Various solutions to the problem of unwanted arcing have been proposed,for example numerous shield designs placed about the cathode are known.Different magnet arrangements have been proposed to ameliorate thisproblem as well, but these solutions have their limitations and unwantedside-effects.

Another aspect of this invention is the provision of a cathode inconjunction with the described anode that essentially reduces any arcingto near zero or acceptable levels that do not have deleterious effectson the substrates being coated. The cathode in accordance with thisinvention together with the anode described heretofore provides acoating system that is highly reliable and requires very little downtime. The combination of the anode and cathode disclosed here provides acoating mechanism that is unsurpassed by other known coating chambers.

Various prior art designs have been proposed to lessen unwantedsputtering at the cathode sides; for example providing electricallyinsulated shields, and various other forms of shielding;notwithstanding, most of these are not satisfactory. One known system isdisclosed in U.S. Pat. No. 5,851,365. Systems of this type generallyprovide a dark-space shield that covers part of the target surface toprevent sputtering from the target mounting fixture. This typicallycauses a substantial amount of the coating to be deposited on the edgeof the shield. In U.S. Pat. No. 5,851,365 a great deal of effort wasdirected to the shape of the shield, but it was found afterwards thatsome coating would build up and eventually fall back onto the targetcausing arcing which resulted in an increase in defects on the coatedsubstrate. This is a significant problem especially for a load-locksystem where the goal is to keep the machine at vacuum as long aspossible. With coating build-up on the lower side of the dark-spaceshield and from re-deposited material onto the target surface, thedark-space itself decreases and sputtering from insulating material setsin which can result in substantial and significant unwanted arcing.

Other shielding solutions have been proposed, for example, U.S. Pat. No.5,334,298 provides a cathode and shield where the marginal areas of thetarget lying outside the erosion zone are covered over by an extensionof the dark space shield. In this embodiment the dark space shield iselectrically floating and is separated from the target by a gap which isso large that no plasma can ignite between the target and the dark spaceshield. Although this arrangement appears to provide some advantagesover others, it is sputter material specific and thus is relativelycostly to implement.

In accordance with an aspect of this invention, a more elegant solutionis provided which is relatively inexpensive to implement since it isfound to work for multiple sputter materials and is believed to besuperior to other prior art solutions.

Turning now to FIG. 11, a cathode 130 is shown with an anode 140,wherein gas is fed into the chamber, away from the cathode through theanode. This avoids high pressure in small volumes close to the cathodewhere the magnetic field is high, for example between the dark-spaceshield and cathode where sputtering has to be prohibited. Preferably theanode opening is at least 2 inches away from the cathode to enable auniform pressure distribution over the target area. The anode voltagehas been found to be insensitive to the distance between anode andcathode. Since this embodiment does not require a dark space shield,this eliminates coating flakes falling on the targets from a dark-spaceshield which typically extends into the flux of sputtered particles.When dark space shields are provided, the relatively sharp edge of theshield also leads to charge build-up, especially when coated withdielectric material, which too causes arcing. In this preferred cathodeembodiment the sides of the cathode are electrically insulated. Theelectrical insulation 142 can be accomplished by the use of insulatingmaterials or through application of an insulating coating. Thedielectric coating can be a dense alumina applied through a plasma spraycoating process. The cathode can be insulated by way of being coatedwith a layer of Kapton™ tape. Alternatively the cathode can be mountedon an insulating material such as Teflon™ or a ceramic. Alternativelysides of the cathode can be exposed to normal atmosphere where airbecomes the electrical insulator. Combinations of above mentionedtechniques can be used to insulate the cathode. Furthermore, extendingthe body of the cathode laterally so as to lessen the magnetic fieldthat extends beyond the cathode body reduces the arcing. By insulatingan extended cathode by plasma spraying alumina on its side andinsulating the bottom with a Teflon™ plate it is possible to reduce thearc rate from >100 arcs/s to <0.1 arcs/s for the same deposition rate.This is a very inexpensive yet effective solution to the problem ofunwanted arcing. The cathode in accordance with this invention can beused for metallic and dielectric coatings. The cathode can be drivenwith any electrical mode (RF, DC, pulsed DC, MF, dual cathode-AC, singlecathode AC).

In summary, a novel container-like anode and coated cathode are providedthat are unlike any known heretofore. Although individually, the anodeand cathode are believed to be novel and inventive, they both contributeto provide a coating system that is highly advantageous. The embodimentsshown are merely exemplary and numerous others may be envisaged withinthe spirit and scope of this invention.

What is claimed is:
 1. A sputtering apparatus for use in the sputteringof a material, comprising: a cathode electrically coupled to a voltagesource; at least one anode defining a substantially closed vesselcomprising one or more sidewalls and a bottom wall, said vessel havingan opening to an electrically conductive inner body and having an outerbody, wherein the inner and outer body are at a same electricalpotential and are formed of the one or more sidewalls and bottom wall,such that the inner body is the inside one or more sidewalls and bottomwall of the vessel and an outside one or more sidewall forms the outerone or more sidewalls and outer bottom wall of the vessel, wherein theelectrically conductive inner body is coupled to the voltage source forproviding a voltage difference between the sputtering material and theconductive inner body, wherein the inner body of the vessel is forreceiving and collecting electrons or negatively charged particlespassing through the opening, wherein the opening to the electricallyconducting inner body is so located for communicating with a coatingchamber and wherein the anode is electrically isolated from the coatingchamber, wherein the opening of the vessel is polygonal shaped, whereinthe cathode is negatively biased and wherein the anode is positivelybiased, the cathode and the anode forming a part of a same electricalcircuit; wherein the opening is at one end or side face thereof, forcommunicating with a coating chamber and for allowing charged particlesto flow between the electrically conductive inner body and the cathodeexternal to the anode and within the coating chamber, and wherein theopening is at least two inches from a cathode within the coating chamberto facilitate a uniform pressure distribution over a target area,wherein the cathode is not within or encircled by the anode; and whereinthe opening has a diameter or largest opening length of “a” and whereinthe opening is a distance “d” from the cathode, and wherein an angleα=arctan (a/d) and wherein α<90 degrees.
 2. A sputtering apparatus anodeas defined in claim 1 wherein the conductive inner body of the anode isat a higher potential than the inner walls of the coating chamber sothat a majority of electrons will preferably flow to the inside of theanode rather than to the inner walls of the coating chamber.
 3. Asputtering apparatus anode as defined in claim 2, wherein the vessel hasan inlet port for receiving an inert gas for igniting plasma in thepresence of a sufficient voltage applied between the electricallyconductive inner body and the cathode, and wherein the positivepotential is at least 5V above ground.
 4. A sputtering apparatus anodeas defined in claim 1 adapted to be disposed outside of the coatingchamber and physically coupled thereto such that the opening of thevessel is facing and open to the coating chamber.
 5. A sputteringapparatus anode as defined in claim 1 wherein the outer body of thevessel is covered with a first material that is different than the innerbody of the vessel.
 6. A sputtering apparatus anode as defined in claim5, wherein the first material is an insulating material.
 7. A sputteringapparatus anode as defined in claim 1 wherein the anode inner body iscoupled to a switch for selectably floating, biasing or grounding theinner body.
 8. A sputtering apparatus anode as defined in claim 1wherein the opening is substantially smaller than a circumference of thevessel so that charged particles can flow between the inner body of thevessel and a cathode and such that coating material is substantiallyimpeded from being deposited into the vessel.
 9. A sputtering apparatusanode as defined in claim 1 fixedly coupled to an outside of a coatingchamber such that in operation during coating, the anode serves as aconducting container and wherein charged particles flow between thecathode in the coating chamber and the inside of the vessel for coatinga substrate disposed in the coating chamber with the material.
 10. Asputtering apparatus anode as defined in claim 1 wherein the opening hasan area of >10 cm2.
 11. A sputtering apparatus anode as defined in claim10, wherein the opening is substantially circular and greater than 15cm2.
 12. A sputtering apparatus anode as defined in claim 1, wherein theinner body is comprised of copper.
 13. A sputtering apparatus anode asdefined in claim 1, wherein the inner body is comprised of stainlesssteel.
 14. A sputtering apparatus anode as defined in claim 1 wherein aninside of the vessel is substantially cylindrical or spherical in crosssection.
 15. A sputtering apparatus anode as defined in claim 1, whereina surface area of the conductive inner body is at least 300 cm2.
 16. Asputtering apparatus anode as defined in claim 3, wherein the pressurein the anode cavity is at least 20% above the pressure in the coatingchamber.
 17. A sputtering apparatus anode as defined in claim 3, whereinthe pressure in the anode cavity is at least two times above thepressure in the coating chamber.
 18. A sputtering apparatus anode asdefined in claim 1 wherein the opening has an area of 15 cm2 to 30 cm2.19. A sputtering apparatus anode as defined in claim 1, wherein asurface area of the conductive inner body is at least 1200 cm2.